Alloys and rectifiers made thereof



July 30, 1957 K. LARK-HoRovlTz ETAL 2,801,376

ALLOYS AND RECTIFIERS MAE THEREF 2 Sheets-Sheet l Original Filed July15, 1945 July 30, 1957 K. LARKHoRovlTz ETAL 2,801,376

Alloys AND REmmERs MADE THEREOF 2 Sheets-Sheet 2 Original Filed July l5.1945 e sts- @ya United States Patent O ALLOYS AND RECTIFIERS MADETHEREOF Karl Lark-Horovitz and Randall M. Whaley, Lafayette,

Ind., assignors to Purdue Research Foundation, Lafayette, Ind., acorporation of Indiana Original application July 13, 1945, Serial No.604,744, now Patent No. 2,514,879, dated July 11, 1950. Di vided andthis application December 29, 1949, Serial No. 135,748

This application is a division of application, Serial No. 604,744, tiledluly 13, 1945, and now Patent 2,514,879.

The present invention relates to an improvement in alloys of germanium,and more particularly to rectiers of electricity, which olfer lowresistance to current tlow in one direction therethrough and highresistance to current ow in the opposite direction, made of such alloys.

In the detailed description of our invention following hereinafter, itwill be observed that several of the elements which may be combined withgermanium are not metals so that the resultant materials are not alloysin the common meaning of the word. However, for purposes of the presentdisclosure, it is to be understood that the word alloy of germanium" asused herein, means to include a union of two or more elements, one ofwhich is germanium, and the other or others being metals, nonmetals, orgases, and the combination of which exhibits electrical properties suchas are found in metals and semiconductors.

The known contact rectiers, i. e., rectitiers comprising suitable metalelectrodes, and a semi-conductor have at least one of the followingdisadvantages:

l. Inability to withstand in continuous use voltages in the back or highresistance direction greater than about 10 volts without permanentinjury to the rectifier.

2. Inability to pass sufficient current in the forward direction forsatisfactory operation of associated apparatus.

3. Low back resistance prohibiting use of the rectifier in highimpedance circuits, that is, circuits over about 100,000 ohms.

4. Seriously decreased eiliciency in rectifying at frequencies greaterthan about l to megacycles.

5. Capacity too high to allow efficient operation at frequencies greaterthan about 5 megacycles.

Due to the aforesaid deficiencies of these known contact rectiliers, theart turned to widespread use of vacuum tube diodes for rectifyingalternating currents. However, vacuum tube diodes, while overcomingcertain of the aforementioned disadvantages of the known contactrectiers, in turn have the following disadvantages:

l. Inter-electrode capacities which are seriously objectionable at highfrequencies.

2. Low forward direction conductance.

3. Requirement of power for heating a cathode.

4. Require a large amount of space as compared to a.v

2,801,376 Patented July 30, 1957 "ice which are capable of withstandingvoltages in the back direction of an order approaching 200 volts.

2. Low forward resistances, for example 30 to 100 ohms at one volt.

3. High back resistances, at about 4 volts ranging from about 10,000ohms to several megohms.

4. May be used with frequencies up to megacycles and will still rectifyat 3,000 megacycles.

5. Provide rectilers of low capacity of about 0.5 micromicrofarad.

6. Less than 50 percent decrease in peak back voltage when ambienttemperature increases from 23 C. to C.

7. Do not require power for heating a cathode; and

8. Do not require more space than about that needed for a commonone-half watt carbon resistor.

The germanium alloys herein disclosed are all of the class of N-typesemi-conductors, i. e., semi-conductors which when made into contacttype rectiiiers present a high resistance to current tlow across therectifying contact when the semi-conductor is positive and thecontacting metal electrode or Whisker is negative, and a lowerresistance when the potential is reversed.

The various germanium alloys of our invention will be described andcompared according to the properties they exhibit when made into contacttype rectiers. Specic electrical properties hereafter referred to are:

Peak back voltage-The voltage-current characteristics measured onrectiers using the alloys of our invention show a voltage peak in theback or high resistance direction. This peak generally occurs within arange greater than 10 volts and approaching the order of 200 volts. Itwill also appear that all of these rectiers using alloys of ourinvention exhibit a negative resistance region in the back direction forcurrents exceeding the current at the peak back voltage.

Back resistance-In the back or high resistance direction these rectiershave resistances ranging from the order of 10,000 ohms to severalmegohms as measured at about 5 volts. High resistances are substantiallymaintained nearly to the peak back voltage.

Forward conductance-The currents passed at one volt in the forward orlow resistance direction for these rectiters generally lie within therange between 5 milliamperes and 40 milliarnperes. Actually, somewhathigher currents may be permitted to pass in the forward directionwithout impairment of the rectifying contact. As will be described laterherein, currents greater than milliamperes are sometimes deliberatelypassed momentarily in the forward direction to produce improvement incertain contact characteristics.

The N-type semiconductors of our invention comprise germanium havingsmall amounts of one of the following elements or certain combinationsthereof alloyed therewith:

Copper and silver of column I of the periodic table;

Magnesium, calcium, zinc, strontium, cadmium, or barium of column II ofthe periodic table.

Titanium, tin, or lead, of column IV of the periodic table;

Nitrogen, vanadium, columbiurn, tantalum, or bismuth of column V of theperiodic table;

Chromium or uranium of column Vl of the periodic table;

Cobalt, nickel, or palladium of column VIII of the periodic table.N-type semi-conductors of germanium may also be formed by alloying smallamounts of, for example, phosphorous, arsenic, or antimony withgermanium, but in rectifiers using such semi-conductors it has beenfound that excessive currents pass at voltages greater than about 3 to10 volts in the back direction which permanently injure the rectifyingContact. It will be understood therefore that our present invention onlyrelates to semiconductors of the N-type which exhibit high back voltagecharacteristics in excess of at least volts, and does not concern allN-type semi-conductors consisting of an alloy of germanium, as forexample, the group last referred to.

Other features and advantages of our invention will appear from thedetail description.

Now, in order to acquaint those skilled in the art with the manner ofmaking alloys in accordance with our invention, and the utilizationthereof as rectifiers of electricity, we shall describe in connectionwith the accompanying drawings and the tables following hereaftercertain of the processes used in making the alloys which lie within ourinvention.

In the drawings:

Figure l shows the voltage-current characteristic curves of severalrectiers using certain of the alloys of our invention, which curves arenot to be taken as typical of given alloys but merely to represent thetype of characteristic exhibited by such alloys in general.

Figure 2 is a graph illustrating the electrical characteristics ofrectifiers using different types of surfaces on one alloy of ourinvention.

Figure 3 is a sectional view of a rectifier, the semiconductor of whichcomprises an alloy of our present invention.

Each alloy represented by the curves of Figure l is designated by a codenumber. The latter part of each code denotes the amount in atomicpercent of the particular element or elements added to germanium toproduce that alloy. No atomic percentage figures for the addition ofnitrogen to germanium are given since it is dicult to determineaccurately the amount or number of nitrogen atoms alloyed with thegermanium.

In the following Table I there are set forth minimum, average, andmaximum values of peak back voltage and forward current obtained onrectifying contacts using certain germanium alloys which we have made inaccordance with the general procedure to be described later. The amountof the added element alloyed with germanium is set forth for each meltin atomic percent, i. e., the proportionate number of atoms in percentof the elements added to the total number of the atoms of germanium andadded elements present. For purposes of adequately setting forth andclaiming our invention, these additions to germanium are to beunderstood as being included in the term Group A" used hereinafter.Substantially all melts in which the addition consisted of a singleelement made to date in accordance with our invention are contained inTable I. It will be observed from that table that a large number ofmelts with certain added elements were prepared and it will beunderstood that the results given are the average results of all of themelts in each instance. It is to be understood, however, that the spreador range of values given in connection with each of the elements addedto germanium might not be true for any particular melt of such additionagent. Characteristics for rectifying contacts on any given alloy willlie somewhere within the range given. Further, all points on any givenalloy listed in Table I and Table II, referred to hereinafter, will notexhibit the same electrical characteristics. Points may be found on eachof the alloys disclosed at which the peak back voltages, backresistances, or forward currents lie in the lower regions of the rangesgiven above for these values. Also on the same surface of each alloyother points of contact may usually be found with electricalcharacteristics which lie toward the upper limit of the ranges above setout. However, as will later be discussed in more detail, some of thealloys are of greater uniformity than others with respect to rectictaioncharacteristics.

4 TABLE I Additions t0 germanium [In atomic percerm] Peak Brick VriltagcForward Current (Volts) at one volt D. C. Addition and percentages(Mllliamperes) Min. Avn. Max. Min. Ave. Max.

Ba; .40, .50 i5 50 125 7 13 i9 Bi: 1.0,.20, 1.25, .70, .28, .20, .31,

.40, .20, .80, .80 i5 50 125 7 13 i9 0d: .90, .30 20 50 105 8 i2 i5 Ca:2.0, 1.35, .80, .50, .50, .28, .28,

.80, .80 25 75 150 5 15 25 Cr: .045, .50 5 15 25 5 15 25 C0: .50 20 3035 10 15 20 Cb: .20, .43, .045 i5 25 40 5 15 40Cu:.00,200,.42,.i0,.34,.37,.40 15 40 75 i 5 40 Pb;3.0,.30,.50,.i3,1.08,.35 25 70 135 i 15 25 Mg:3.0,3.0 i0 00 ii5 2 10 20 Ni: 1. 5,.10, .50, 1.0, 1.0, 1.0, 1.0,

1.0 20 50 90 7 15 30 N2: Solldled in Ni at pressures M2, i8, 600,51151750, mmHg.. 20 80 100 7 i0 25 Pd:.50,.50 05 110 5 15 25 8585,50 2540 80 7 10 20 Sr: .50, .50, .80, .80, .80, .50, .50,

. ,.0 25 75 150 5 10 25 Ta: .44 20 40 70 3 15 30 Sn; .50, .45, .82, .50,.50, .25, .05,

.40, .40, .40, .40, .40, .40, .40 25 75 150 2 15 30 Ti; .50, .50 10 3070 a 7 15 U: .09, .09... 20 25 50 2 5 20 V: 1.0, 10 25 55 i0 25 40 Zn:.00, 25 50 100 5 i2 20 In Table II below there are set forth the meltsin which two elements have been alloyed with germanium. The

additions of these combinations of elements are also set forth in atomicpercent as previously defined. lt will be understood that the alloys setforth in this table are also to be included 1n the term Group A abovereferred to for purposes of claiming our present invention. The

peak back voltages and the forward currents at one volt of rectiers madeof these alloys are also set forth in this table.

TABLE II Melts of more than one addition to germanium Peak Back ForwardCurrent` Additions and Percentages Voltage at one volt` (Volts)(Milliampervs) Min Ave Max. Miri. Ave. Mar

.3500, .70sn 25 40 150 i5 20 30 .2100, .65Sii 15 50 80 i5 22 50 neonataThe germanium alloys of our invention may be prepared in all Ycasesexcept for the germanium-nitrogen alloy, by melting pure germanium withthe desired alloying element or combination of elements in either a highvacuum of the order of 10-5 mm. mercury at about 1000 C. or in anatmosphere of helium. Precaution should be taken to prevent theaccidental introduction of unknown and perhaps detrimental impuritiesinto the melt from sources such as the crucible or boat in which theingredients are disposed for melting, the furnace itself, or somematerial volatilized in the furnace. Alloying germanium with nitrogenmay be effected by melting the germanium in an atmosphere of nitrogenwhich may be either purified nitrogen or nitrogen direct from acommercial cylinder. The germanium is melted in nitrogen at pressuresranging from about 2 mm. to 760 mm. Hg at a temperature of 1000 to 10.50C. Good results appear to be independent of pressure and melts preparedwithin the above range of pressures were all satisfactory.

The germanium successfully used for these alloys had purity approaching100%, and electrical resistivity greater than about one ohm cm. Thegermanium which we have successfully alloyed with other elements to formthe alloys listed in Tables I and II was prepared from GeOg obtainedfrom the Eagle-Fieber Lead Company of Joplin, Missouri. The oxide wasreduced in an atmosphere of commercial hydrogen at temperatures of 650to 700 C. over a period of three to four hours. The oxide reduced inthis manner leaves the germanium metal in the form of a gray-greenpowder which is then alloyed with another element or elements in themanner and proportions described.

The aforesaid melts of germanium and the added element or elements wereheld in the molten state long enough to allow mixing of theconstituents, and it has been found that about 5 to 15 minutes issufiicient for this purpose. Usually ingredients to form melts of aboutlive to six grams each were used in proportions above set forth indetail. After the constituents had been allowed to mix, the melts wereallowed to solidify and cool which was accomplished either byimmediately removing heat or by controlled cooling apparatus. In certaincases the uniformity of the melt is aifected by the manner in which itis cooled. These variations will be discussed later.

A specific melt in accordance with our invention was prepared asfollows:

Pure GeOz was reduced in hydrogen at atmospheric pressure for aboutthree hours at 650 to 700 C. Six grams of pure germanium powder soobtained were then placed in a porcelain crucible together with smallflakes of pure tin amounting to 25 milligrams or about 0.8 atomicpercent of tin.

The crucible and contents were then placed inside a graphite cylinderused as a heater in the high frequency field of an induction furnace,and lowered in a vertical quartz tube which was then evacuated andmaintained at a pressure of about 5 mm. mercury. Power was then appliedto the external coil of the induction furnace to melt the germanium andhold it molten for about 5 minutes. The melt was then allowed to cool bymerely turning ol the power to the coil. Thereafter wafers were cut fromthe alloy, and were soldered with softsolder to a suitable metalelectrode to produce a very low resistance non-rectifying contact withone face of the wafer. The exposed face was then ground with 600 meshalumina and etched for 2 minutes with an etching solution consistingessentially of HNOa, HF, Cu(NOs)2 and water in proportions to be laterdescribed herein. These wafers were then assembled in suitablecartridges each provided with a conventional metal electrode or Whiskerwhich wasused to contact the alloy surface. Across the rectifyingcontact thus produced we obtain the electrical characteristics describedabove.

As mentioned in the above specific example, the surfaces ofthese alloysare usually ground Vliat and then etched in a manner to be described indetail, However, as hereinafter related, the etching of the alloysurfaces is not essential since, for example, by breaking open a melt,points may be found which exhibit the aforementioned electricalrectifying characteristics. Such broken surfaces present geometricallyirregular faces which introduce some diiculty in assembly of therectifiers. Thus, grinding the alloy surface flat and etching it appearsto be the most feasible manner of producing the rectiers in thecommercial practicing of our invention.

From the above Table I it will be observed that the majority ofexperimental work conducted in the development of our invention has beenwith the alloy germaniumtin. In connection with our experimental workwith tin it has been found that above 0.1 atomic percent of tin content,the amount of tin added is not critical. Germanium containing aboveabout 0.1 percent tin usually shows tin separated out, both at internalgrain boundaries and on the outer surfaces. In some melts containing tinin excess of 0.1 atomic percent, ductile layers of this tinrich materialwere frequently observed, particularly in the lower regions of the melt.In this connection we wish to observe that in making the germanium-tinalloys it is desirable in producing the melt that the boat or cruciblein which the elements are contained be gradually removed from the hotfurnace region. This will produce more uniform alloys, particularly ifthe melt is so removed that the top region of the melt is the last partto cool. It appears that germanium becomes saturated at about 0.1percent tin under the melting and cooling conditons used. However, inour experimental work larger amounts of tin were added in order toobserve if such solubility depended upon the amount of tin available;more tin merely segregated. At 17 atomic percent addition of tin, theentire melt was interlaced with tin-rich veins which had metallic lowresistance ohmic conductivity.

With bismuth additions it is diicult to control the amount of bismuthactually remaining in the germanium during the melting cycle. Aconsiderable fraction of the bismuth volatilizes so that quantitiesadded have little relation to the quantities actually remaining in themelt` However, the results indicated in Table I in connection withbismuth were obtained by the addition of bismuth to the extent thereindicated.

After the melts have been made as above described they are suitable foruse as rectifiers of electricity by simply making contact with thesurfaces of such alloys with suitable electrodes or whiskers. in most ofour experimental work a 5 mil tungsten Whisker sharpenedelectrolytically with a tip diameter of less than 0.1 mil was used asone electrode or Whisker, the other electrical contact usually beingmade by soldering the alloy to a suitable conductor. However, tests haveshown that the peak back voltages of rectiers made from the alloys ofour invention are little affected by the metal of which the Whisker ismade. Whiskers made of the following metals have been tried and onlyvery slight deviations were noted over a large number of points ofcontact with the alloys of our invention: Mn, Pt, Ta, Ni, Fe, Zn, Mo, W,Au, Cu, Ag, Zr, Pt-Ir, and Pt-Ru. It appears therefore that choice of aWhisker material may be determined on the basis of requirements otherthan the peak back voltage on rectiers using the alloys. Theseelectrodes or whiskers may have contact with the surfaces of the alloysas formed upon solidication, or on surfaces exposed by breaking themelt. As mentioned above, however, it is desirable to grind and etch thesurface. Thus in one method of producing rectiers using the alloys ofour invention, the melts, which usually were of pellet form 5 to l0millimeters thick, may be cut into thin plates or slabs and a surfacethereof ground with a suitable abrasive such as 600 mesh alumina(A1203). The abrasive used is not critical in that it has been foundthat other abrasives such as C203, M50;

VazOs, SnOz, ZnO and 4-0 paper are equally satisfactory. This may thenbe followed by a further grinding step with fine emery paper althoughthis grinding step mayV be eliminated, if desired, without substantiallyaltering the final product. The surface of the plate or slab is thenetched with a suitable etching solution which in one modification of ourinvention has the following approximate composition:

4 parts by volume hydrouoric acid (48% reagent) 4 parts by volumedistilled water 2 parts by volume concentrated nitric acid 200milligrams Cu(Nos)z to each 10 cc. of solution Such a solution willsatisfactorily etch the surface of the plates or slabs in about l to 2minutes at room temperature and may be applied with either a swab or byimmersing the surface in the solution. This etching is not particularlycritical but care should be taken not to unduly extend the etching sincethen a high polish is produced which may impair the performance of thealloy.

We have also found that other types of etches may be used effectively onthe germanium alloys of our invention in addition to the etching abovedescribed. Modified etching solutions and procedures are as follows:

A solution consisting approximately of 1 gram stannyl chloride in 50 cc.of H2O may be used as an electrolytic bath for etching the alloysurfaces. Immersing the alloy as the anode in this solution will resultin satisfactory etching within about 11/2 minutes at about 2V: voltsapplied.

An alternative modification of an electrolytic etching solution maycomprise parts concentrated HNOa and S0 parts H2O by volume. Using thealloy as the anode for about 11/2 minutes at l to 2 bolts will result ina satisfactory etch.

Reference may now be had to Figure 2 of the drawings illustrating theeffect of etching of one of the alloys of our invention. The alloyselected to illustrate the effect of etching is identified as melt24P-OUl36-.25Sn- This melt as appears from the aforesaid designationconstitutes .25 atomic percent tin. The curve identified by referencenumeral l illustrates the electrical characteristic of the germanium-tinalloy above identified in which the surface was ground with 600Al203 butnot etched. The curve indicated by the reference numeral 2 illustratesthe electrical characteristics which were obtained on a freshly brokensurface of an alloy of the above composition but which surface has notbeen etched. Curve member 3 illustrates the electrical characteristic ofa surface ground with 600Al2O3 and then etched in accordance with themanner first described.

The curve indicated by the reference numeral 4 illustrates electricalcharacteristics of another point on the alloy after etching as describedin connection with curve 3, the curves 3 and 4 representing the best andpoorest performances, respectively, of the particularly germanium tinalloy above identified, after etching. It is to be observed that in thisgraph the voltage scale in the forward direction is there expanded by afactor of as compared to the voltage scale indicating the high backvoltage characteristics of the alloys of our invention. As indicated,the currents are given in milliamperes.

It will be observed from an examination of Figure 2 that the electricalcharacteristics of a rectifier using a broken surface exhibit high backvoltages and forward conductances within the range of values obtainedwhen using a ground and etched surface. However, such broken surfacesare shiny and geometrically irregular so that the Whisker tends to skidwhich is undesirable in assembling permanent rectifier units. FromFigure 2 it is apparent that the high back voltage and high backresistance properties are inherent in the alloys and that the etching iseffective for restoring such properties after grinding. Further, we havediscovered that natural surfaces formed when solidifying the alloys invacuum will, if not contaminated or otherwise affected by grinding, givehigh back voltages and high back resistances when mounted and tested inair.

For certain applications of these rectifiers it is desirable that theyhave back resistances exceeding one megohm at about 5 volts. Using theprocedure described above will occasionally produce such high backresistances. However, we have found that a substantial and permanentincrease in the back resistance can be effected by applying poweroverloads across the contact, for short intervals of time, each oflength about 1A to 1 second or longer. The power treatment can beeffected with the use of either alternating or direct current. Bygradually increasing the voltage applied, and hence the current passedby the contact during successive pulses, an optimum value can be foundto produce the maximum back resistance for a given contact. For directcurrent treatment in the forward direction such optimum current valuesrange from about 200 to 800 milliamperes. For alternating powertreatment the optimum values of forward peak current range from about300 milliamperes to 1000 milliamperes. One can apply such alternatingcurrent treatment simply by connecting the rectifier in series with acurrent limiting resistance and the secondary of a transformer.Depending upon the size of this current limiting resistance, values ofl0 t0 40 ohms have been used, voltage pulses ranging from 7 to 60 voltsacross the rectifier and resistance serve to yield the maximum increasein back resistance.

Table III shows the permanent effects of such power treatment upon a fewtypical rectifiers using alloys of our invention and prepared asdescribed. It will be seen from the table that the most significanteffect of the power treatment is the increase in the back resistance asmeasured at about 4.5 volts. This resistance is increased by factorsranging from about 10 to 50 times the values measured before treatment.Relatively minor increases of 10 to 20 percent are effected on the peakback voltage. Forward currents at one volt are in general decreased byamounts ranging from 10 to 50 percent.

TABLE III Effects of power treatment [Values before power treatment arefollowed in brackets by values nfter pow er treatin ont Forward Back Re-Pealr Back Current at sistance at Alloy Used in Rectifier Voltage oneVolt 4.5 Volts (volts) (milli- (niegohms) amparos) 75 uns) 9 4.5) .02(3) 11 6.5) .30 (4) 13 (T) .25 (2.5)

6 (fi) .15 (8) 8 (Si .05 (.8) 24(10) ,U4 (7. 5) 2f) (17) .48 (15) 40(l0) .20 (4) 10 (8i .2D (l) l5 (10.5) .13 (2) 1s (i0) .10 (4) 4 (4) .40(2) 1f] .20 (3) l0 (6.4) .40 (7. 5) 15 (l0) .20 (3) 14 t8) .38 (2.5) 30(16) .81 (3. 9) 16 (1U) 1.0 (7. 5)

It has been demonstrated above that the high back voltage, high backresistance, and good forward conductance properties disclosed areinherent in the germanium alloys of our invention. Modifications ofsurface treatments or power treatments as described above will, however,vary the magnitude of these properties within certain general limits.For example, on a given alloy surface, variations in surface treatmentand power treatment may be expected to vary the average peak backvoltage by a factor of about 2, the average forward curent by a factorof about 2, and the average back resistance by factors up to 50. YItwill be noted that the back resistance is the property most sensitive toVvariations in treatment, particularly to power treatment.

The following Table IV summarizes, on the basis of all melts rnade inexperimental work conducted under our invention, the approximate guresof the minimum, average, and maximum values of peak back voltage andforward current at one volt which might be expected on the germaniumalloys Yconsisting of the addition of a single element.

TABLE IV Peak Back Forward Current Voltage at One Volt Alloy (volts)(mllllamperes) Mln. Ave. Mar. Mtn. Ave. Max.

25 75 150 2 15 30 20 B0 160 'i' l0 25 25 75 150 5 l5 25 25 75 150 5 1025 20 50 90 7 15 30 25 50 100 5 12 20 25 7l) 135 l 15 25 30 55 110 5 1525 10 50 100 2 10 20 2U 50 105 5 12 l5 15 50 125 7 13 20 l5 40 100 l0 l530 25 40 80 7 l0 20 10 3l) 70 3 7 l5 2() 3D 35 10 l5 20 2t] 40 70 3 l530 l5 40 75 l 5 40 It will appear from the above table that the rangesof values for the better alloys appear to be quite similar. Diierencesenter in the manner in which the values, within the ranges indicated,are concentrated. For example, the nitrogen alloys can usually beexpected to have 70 to 90 percent of back peak voltages over 60 volts.Values on tin melts are more uniformly spread within the range of thelimits given above. For the tin melts approximately 50 percent of thepoints on the surfaces thereof will have voltages above 60 volts. Itappears that the pure germanium alloyed with tin or melted in anatmosphere of nitrogen represents the most advantageous alloy. Followingthem, alloys of pure germanium with calcium, strontium or nickel appearto be in order. It is to be understood, however, that one skilled in theart working within the range of the alloys herein disclosed will readilybe able to produce alloys having high back voltage and resistancecharacteristics and good forward conductances.

In Figure 3 of the drawings we have shown one type of rectier in whichour invention may be embodied. In the form of the device there shown awafer 5 which may be of any of the germanium alloy above disclosed ismounted to have a low resistance non-rectifying contact with a metalelectrode member 6. An electrode or Whisker 7 is connected at one end toan electrode supporting member 8 with the end of the Whisker in contactwith the surface of the germanium alloy wafer 5. The standard 9 providesfor mounting the members supporting the wafer 5 and electrode or Whisker7 in insulated relation. The rectifier contemplated by our invention maybe of various forms, the only critical constructional feature being thatthe germanium alloy wafer comprising the semiconductor, and the Whiskerfor contacting the surface of the wafer being arranged and supported sothat one end of the Whisker engages the semi-conductor surface. It isunderstood that suitable leads are connected to the wafer orsemi-conductor and to the Whisker or metal electrode so that the devicemay have application in any desired circuit for use in the rectificationof current.

While we have disclosed what we consider to be the preferred embodimentsof our invention, it will be under# stood that various modifications maybe made therein without departing from the spirit and scope of ourinvention.

We claim:

l. An electrical device comprising a semiconductor, a counter electrodehaving substantially point contact with said semi-conductor and a secondelectrode having an area of contact with said semi-conductor which islarge compared to that of the counter electrode, said semi-conductorconsisting of germanium of the order of 99% purity in combination withat least one of the elements from the group consisting of chromium anduranium, said device having a peak back voltage in the range in excessof l0 volts and approaching the order of 200 volts.

2. An electrical device comprising an alloy formed of a mixture ofgermanium having a purity of the order of 99% and chromium in an amountof between 0.045 and 0.50 atomic percent, and a pair of electrodeelements in contact with said formed alloy, one of said electrodeelements having substantially point contact with said alloy and thesecond of said electrodes having an area of contact which is largecompared to that of the point contact electrode.

3. An electrical device comprising an alloy formed of a mixture ofgermanium having a purity of the order of 99% and uranium in an amountof 0.09 atomic percent, and a pair of electrode elements in contact withsaid formed alloy, one of said electrode elements having substantiallypoint contact with said alloy and the second of said electrodes havingan area of contact which is large compared to that of the point contactelectrode.

4. The method of making an electrical device which comprises mixinggermanium having a purity of the order of 99% with at least one of theelements from the class consisting of chromium and uranium, applyingheat to the mixture to reduce the mixture to a uid state, maintainingthe heat for a time period suciently long to permit mixing of theselected constituents, removing the heat to permit soliditication of themixture, cutting from the ingot formed upon mass solidication wafers towhich contact electrodes may be applied, applying contact electrodes tosaid wafers, securing one of said electrodes to one surface of a cutwafer, locating a second substantially point contact electrode upon adifferent surface of the cut wafer and in substantially point contacttherewith, and then applying electric power between the electrodes andthe wafer by regulating the supplied current in the forward directionthrough the wafer and limiting the current value to the range between200 and 800 milliamperes applied in pulses of between l/4 to 1 second inlength.

5. The method of claim 4 including, in addition, the steps of connectingthe formed device in series with a current limiting resistance and asecondary of a transformer of alternating electric currents controllingthe peak current in the forward direction to the order of between 300and 1000 milliamperes so that the voltage across the device and limitingresistance is of the order of between 7 and 60 volts and the limitingresistance is of the order of l0 to 40 ohms and regulating the period ofapplication of the alternating current to intervals varying between 1Aand l second in time duration.

6. An electrical device comprising a semiconductor, a counter electrodehaving substantially point contact with said semi-conductor and a secondelectrode having an area of contact with said semi-conductor which islarge cornpared to that of the counter electrode, said semi-conductorconsisting of germanium of the order of 99% purity in combination withat least one of the elements from the class consisting of chromium anduranium, said device having a peak back voltage in the range in excessof 10 volts and approaching the order of 200 volts, the back resistanceof said device being in the order of between 10,000 ohms to severalmegohms at about 5 volts and the forward current being in the range ofbetween 5 and 40 milliamperes at one volt in the low resistancedirection of current ow through the device.

7. An electrical device comprising a body of semi-conducting germaniumof the order of 99% purity in combination with at least one of theelements selected from the group consisting of chromium and uranium, anda pair of electrodes in electrical contact with said body, said chromiumbeing present in an amount up to 0.5 atomic percent and said uraniumbeing present in a amount up to 0.09 atomic percent.

8. An electrical device comprising a body of semiconducting material anda pair of electrodes in electrical contact with said body, said materialcomprising an alloy formed of a mixture of germanium having a purity ofthe order of 99% and chromium in an amount of between 0.045 and 0.50atomic percent.

9. An electrical device comprising an alloy formed of a mixture ofgermanium having a purity of the order of 99% and uranium in an amountof 0.09 atomic percent, and a pair of electrode elements in electricalcontact with said formed alloy.

10. A method of making an electrical device comprising alloying with aquantity of germanium semi-conducting material a small quantity of animpurity substance in order to impart to said germanium predeterminedconductivity characteristics, cutting a wafer from the alloy thusformed, applying an electrode to a surface of said wafer, applying asubstantially point contact electrode to another surface of said wafer,and applying an electric power overload between said point contactelectrode and said Wafer for a short interval of time.

11. A method of making an electrical device comprising applying anelectrode to a surface of a body of a semiconducting material comprisinga germanium alloy, applying to another surface of said body asubstantially point contact electrode, and applying electric poweroverloads between said point contact electrode and said body for shortintervals of time.

12. The method of claim ll including, in addition, regulating thesupplying current in the forward direction through the body and limitingthe current value to the range between about 200 and 800 milliamperesapplied in pulses of between about 1A second and 1 second in length.

13. The method of claim 12 including, in addition, controlling the peakcurrent in the forward direction to between about 300 and 1000milliamperes so that the voltage across the device is of the order ofbetween 7 and 60 volts.

14. A method of treating an electrical device comprising a body ofgermanium semi-conducting material and a substantially point contactelectrode in contact with a surface of said body, comprising applying anelectric overload between said point contact electrode and said body fora short interval of time whereby to effect substantial improvement inthe rectification properties of said device.

l5. An electrical device comprising a body of semiconducting materialand a pair of electrodes in electrical contact with said body, saidmaterial comprising an alloy formed of a mixture of germanium having apurity of the order of 99% and chromium in an amount up to about 0.05atomic percent.

16. A11 electrical device comprising a body of semiconducting materialand a pair of electrodes in electrical contact with said body, saidmaterial comprising an alloy formed of a mixture of germanium having apurity of the order of 99% and uranium in an amount up to about 0.09atomic percent.

17. The method of making an electrical device which comprises mixinggermanium having a purity of the 0rder of 99% with at least one of theelements from the class consisting of chromium and uranium, applyingheat to the mixture to reduce the mixture to a uid state, maintainingthe heat for a time period suciently long to permit mixing of theselected constituents, removing the heat to permit solidication of themixture, cutting from the ingot formed upon mass solidification wafersto which contact electrodes may be applied, etching a surface of saidwafers in a solution made up of approximately 4 parts by volume ofhydrofluoric acid (48% reagent), 4 parts by volume of distilled water, 2parts by volume of concentrated nitric acid, and 200 milligrams Cu(NOs)2to each l0 cc. of solution for a time period in the general range ofbetween 1 and 2 minutes, and applying contact electrodes to said wafers.

18. The method of making an electrical device which comprises mixinggermanium having a purity of the order of 99% with at least one of theelements from the class consisting of chromium and uranium, applyingheat to the mixture to reduce the mixture to a fluid state, maintainingthe heat for a time period sufficiently long to permit mixing of theselected constituents, removing the heat to permit solidification of themixture, cutting from the ingot formed upon mass solidication wafers towhich contact electrodes may be applied, electrolytically etching one ofsaid wafers as an anode in a solution in the proportions ofapproximately 1 gram stannyl chloride to 50 cc. water for about 1%/2minutes at about 2% volts, and applying contact electrodes to saidwafer.

19. The method of making an electrical device which comprises mixinggermanium having a purity of the order of 99% with at least one of theelements from the class consisting of chromium and uranium, applyingheat to the mixture to reduce the mixture to a uid state, maintainingthe heat for a time period sufficiently long to permit mixing of theselected constituents, removing the heat to permit solidication of themixture, cutting from the ingot formed upon mass solidication wafers towhich contact electrodes may be applied. electrolytically etching one ofsaid wafers as an anode in a solution in the proportions ofapproximately S parts concentrated nitric acid to 50 parts water byvolume for about 11/2 minutes at about l to 2 volts, and applyingcontact electrodes to said wafer.

References Cited in the tile of this patent UNITED STATES PATENTS

1. AN ELECTRICAL DEVICE COMPRISING A SEMICONDUCTOR, A COUNTER ELECTRODEHAVING SUBSTANTIALLY POINT CONTACT WITH SAID SEMI-CONDUCTOR AND A SECONDELECTRODE HAVING AN AREA OF CONTACT WITH SAID SEMI-CONDUCTOR WHICH ISLARGE COMPARED TO THAT OF THE COUNTER ELECTRODE, SAID SEMI-CONDUCTORCONSISTING OF GERMANIUM OF THE ORDER OF 99% PURITY IN COMBINATION WITHAT LEAST ONE OF THE ELEMENTS FROM THE GROUP CONSISTING OF CHROMIUM ANDURANIUM, SAID DEVICE HAVING A PEAK BACK VOLTAGE IN THE RANGE IN EXCESSOF 10 VOLTS AND APPROACHING THE ORDER OF 200 VOLTS.